1. Field of the Invention
The present invention concerns an apparatus and a method for sampling from a product flow, where the sampling is performed continuously and where the product is collected in a cup, the cup being introduced directly into the product flow for subsequently determining weight in relation to volume or other physical conditions of the product, and wherein the cup is emptied after ending the sampling.
2. Description of Related Art
It is common knowledge to perform sampling, e.g., measuring density of products, such as, e.g., expanded and heat treated products, but also of other products where the products appear with a certain porosity during the manufacturing process, and where the product is desired to be continuously weighed in order thereby to regulate the processes controlling the expansion and thereby the porosity of the weighed product.
Density measurement is presently performed in various ways. Systems that are based on a specifically defined volume which is filled with products and weighed subsequently is the most widely used technique. This technique is frequently used at a purely manual level, where a process operator manually fills a tared container with a known volume with products. The container is often a traditional household measuring glass with closed bottom which is overfilled with product and subsequently leveled at the top such that the defined volume is completely filled with products. Subsequently, the container is weighed and the weight of the product in the defined volume may thereby be determined. This method of determining the density of a given product is used in production processes within many different industries, such as, e.g., processes for making food for animals, breakfast cereals, snacks, metal powder, fertilizer, wood and plastic.
During the making of these different products, which often occurs under high temperature by means of a compacting or extruding machine, the process parameters can be changed such that the texture of the given product is changed, entailing a change of the density of the product as well. A given product will frequently have a specific volume which is intended. This may, e.g., be in connection with filling of bags of a given product where a given density of a product is wanted in order thereby to optimally fill a package. By changing the addition of energy, moisture or similar process parameters for making a given product, the characteristic of the product can be changed and thereby also the density of the product. A process operator will therefore continuously check the density in order thereby to regulate the process if the density deviates from the specified value.
The problem of manual sampling or density measurement is that the repeatability is not great enough and that the weighing result therefore can only be used as an indication and not as a completely true value. This is due to the fact that a process operator is not able to fill a given sampling container in a uniform way. On this background, it has previously been attempted to construct automatic systems which may perform a continuous uniform sampling and weighing of the products. These systems are satisfactory for specific products and sizes of products; however, in industries as, e.g., those making snacks, breakfast products and feed for animals, the products are often relatively large and have a tendency to become sticky as a result of the heating process by which the product is formed.
The best known prior art for density weighing is based on a sampling cup with a closed bottom. The sampling cup is mounted on an arm which may be displaced horizontally and which is mounted on a weighing cell. The sampling cup is moved into a give product flow whereby the cup is (over)filled with product. When the cup is retracted to the weighing area, the sampling cup is scraped clean at the top in order to provide a defined volume of the product to be weighed. When the sample has been weighed, the cup is turned such that the product is emptied from the sampling cup. The prior art, however, has certain drawbacks that frequently cause the weight obtained to be as inaccurate as manual weighing, so that it can only be used as an approximate result. The drawbacks are the following:
1. The sampling cup with closed bottom. In density measurement of hot pellets, which is often the product, though not limited to such, the temperature of the product immediately before density measurement will often be about the boiling point of water as a result of the heating process. The density in the manufacturing process is flexible and easily influenced. By collecting a given sample for measurement, a condensation of vapor will start during collecting in the cup. The product as well as dust and crumbs will stick to the cup upon emptying. After some time, deposits will appear in the sampling cup which will cause the presumed volume in the sampling cup used for collecting the product to be reduced, and the weighing result thereby will no longer be accurate.
Attempts to clean the sampling cup, either with compressed air or rotating brushes, have not appeared to be sufficiently effective.
2. Scraping the sampling cup is an essential part of the system. The more homogenous scraping of the sampling cup is, the more precise weighing. As the prior art uses a cup with a closed bottom, it requires a large diameter in order to achieve a reasonable volume for the product, at the same time generating a large scraping area and thereby leading to fluctuating measuring results. In general, the best weighing result is achieved by the largest possible volume and the smallest scraping area in the sampling cup. Since the products are often hot and sticky, scraping of the sampling cup can imply that large lumps are entrained, causing large deviations in the weighing result.
3. Hygiene is essential in manufacturing processes for products forming part of the food chain. Since cleaning cannot be done efficiently by the prior art, either by the product flow or in other mechanical ways, a hygiene problem arises whereby bacteria cultures as e.g., salmonella can appear.
4. The installation height of a given density measuring apparatus is very critical as many processing plants have very little spacing between two processing machines available. The prior art is very space consuming due to the technical embodiment, where compensation is made for the design of the sampling cup with closed bottom by increasing the diameter and the height, respectively, and large changes in the processing plant are therefore required, if possible at all.
An apparatus is known from DE 199 09 437 for taking a sample in a product flow where the sample is taken by a sampling cup with an upper and a lower plate that close and open the filling and emptying openings, respectively. This sampling cup is cleaned by compressed air which partly may provide for the cleaning of the sampling cup. However, there is the disadvantage that possible accumulation of residues of a sticky product cannot entirely be avoided, entailing that it is required with a regular manual cleaning of the sampling cup.